1. Field of Invention
The present invention is directed generally to a system and method for controlling ignition spark for a combustion engine and, more particularly, to a system and method for optimizing ignition spark based on the engine operating conditions.
2. Description of Background
Modern reciprocating engine control systems are designed to achieve precise control of the fuel-to-air ratio of the charging mixture supplied to the combustion chambers and to control the timing and magnitude of the spark which initiates the combustion process and expansion of the mixture. If the spark occurs too late during the engine cycle, i.e., the spark is too "retarded," or with insufficient energy to achieve a combustion process with the desired rate of flame front propagation, then the combustion and gas expansion process may not be completed before the engine piston has left the power producing portion of that cycle. This may result in less power from the engine, increased fuel consumption, and undesirable levels of exhaust emissions. Conversely, if the spark is too early in the combustion cycle, i.e., the spark is too "advanced," or with too much energy, early detonation of the fuel-air mixture may result, which consequently may cause damaging engine "knock" or excessive cylinder head temperatures, both of which may severely reduce the life of the engine.
Such control is of particular significance for aircraft engines, where it is important for an engine to last a long time, despite the fact that an aircraft engine typically runs "hot" most of its life. For example, aircraft engines are typically designed to operate at relatively low engine speeds to reduce wear and stress on the engine components. Thus, in order to gain the necessary power for flight, the engine cylinders are made relatively large, for example, 1.5 liters. To further enhance durability, when the aircraft engine is cold, because it is relatively difficult to spark the gap of the spark plug, increased spark energy is required to ensure the starting of the aircraft. Conversely, when the engine is hot, less energy is required to spark the gap, allowing engine stress to be decreased by decreasing the spark energy.
Proper control of the ignition spark is made more difficult if the power required to generate the spark is capable of varying over a broad range. In power supplies for aircrafts, for example, the ignition spark typically relies on a twenty-eight volt DC power supply which can typically deteriorate to as low a twelve volts DC during aircraft operation. The power supply is used by an ignition coil to generate a high voltage required by the spark plug to ignite. Because of the vacillation in the voltage supplied to the ignition coil, the ignition spark energy will accordingly vary, resulting in deterioration in the precision of the ignition process.
Modern reciprocating engine control systems utilize digital electronic processors to calculate the desired timing for the ignition spark during the engine cycle based on measured engine operating parameters. Typical relevant art engine control systems do not attempt to vary the intensity of the spark energy, although it may vary significantly over the starting and operational power range of the engine. Further, in the case of an aircraft engine, the spark energy may vary over a wide altitude and speed envelope. In addition, the relevant art engine control sensors do not compensate for variations in electrical power supplied to the ignition coils, except for engines requiring a nominally constant spark energy.
Accordingly, there exists a need in the relevant art for a system and method to optimize and control the spark energy intensity under circumstances of varying electrical power.